This invention relates to a method of controlling the operation of an internal combustion engine, and more particularly, to such method in which the operation of the engine is controlled depending on the intake air temperature thereof.
One example of a method available for controlling the operation of an internal combustion engine is exhaust gas recirculation (EGR) for returning part of engine exhaust gases to the intake system of the engine. However, when a control method of this type is applied under a condition where the fuel supplied to the engine is not sufficiently atomized, the state of fuel combustion within the engine generally will be adversely affected, resulting in a decline in the operating performance of the engine.
Since the degree of atomization of fuel supplied to an internal combustion engine is dependent upon the engine coolant temperature, it has been proposed to sense the engine coolant temperature and initiate the exhaust gas recirculation operation when the sensed value of coolant temperature exceeds a predetermined value of. Such an arrangement is disclosed in e.g. Japanese Provisional Patent Publication (Kokai) No. 61-81568.
A problem with such an arrangement is that a decline in the degree of fuel atomization can occur when the engine intake air temperature is lower than normal (e.g. 15.degree. C. or less), even though the engine coolant temperature is slightly higher than the aforementioned predetermined value. Conventionally, this problem is dealt with by setting the predetermined value of engine coolant temperature to a somewhat high value (e.g. 75.degree. C. ) and starting exhaust recirculation when the engine coolant temperature exceeds this value. An alternative approach is to mount an intake air temperature sensor in the engine intake pipe and suspend the exhaust gas recirculation when the sensed value of intake air temperature is lower than a predetermined value.
However, the former attempt at a solution delays the start of control and results in a deterioration in an exhaust gas scrubbing function. The latter approach involves control equipment of some complexity and is impractical in terms of cost as well.